Method and apparatus for detecting defects along the edge of electronic media

ABSTRACT

An electronic media edge defect detector in one form has plural light sources and detectors arranged to direct and receive deflected light from the side edge margins and outer edge margins of the electronic media. The detected light is analyzed to detect the presence of defects. Individual wafers may be raised while in a cassette and turned during the inspection without removing the wafers from the cassette.

CROSS REFERENCE

This application is based on Provisional Patent Application No.60/216,597, filed on Jul. 7, 2000, entitled, “Method And Apparatus ForDetecting Defects Along The Edge Of Electronic Media”, by John Howells,Alan J. Swan and Thomas J. Hafner, and Provisional Patent ApplicationNo. 60/217,063, filed on Jul. 10, 2000, entitled, “Method And ApparatusFor Detecting Defects Along The Edge Of Electronic Media”, by JohnHowells, Alan J. Swan and Thomas J. Hafner. The entire disclosures ofthe above mentioned provisional applications are hereby incorporated intheir entirety by reference herein.

SUMMARY

The present invention relates to a method and apparatus for, among otheraspects, inspecting and determining the presence of defects along theedge of electronic media. For purposes of this description, the term“electronic media” refers to data storage media such as hard disks,DVDs, CD ROMs and the like, and also encompasses other media whichcontains or is to contain circuits and/or electronic information ordata, such as semi-conductor wafers. The media may assume a variety ofshapes although a specific embodiment described below has particularlyapplicability to electronic media in disk form.

Electronic media such as semi-conductor wafers in disk form may containdefects at the outer edge and along both side edge margins of the wafer.These defects can take various forms such as chips, cracks, scratchesand marks on the surfaces near the edge of the wafer.

By determining the presence of defects, decisions can be made whether todiscard the electronic media or process it in a way that avoids thedefect containing portion of the media.

A need exists for an improved method and apparatus for detecting defectsalong the edge and edge margins of electronic media such as electronicinformation storage and/or circuit containing disks. The presentinvention is directed toward new and unobvious acts, steps and featuresas described below, both alone and in combination with one another.Thus, the invention is not limited to a method or apparatus whichcontains all of the features or addresses all of the advantagesdescribed below in connection with various embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one form of an electronic media defectdetection apparatus and in particular is illustrated in connection withdetecting defects along the side edge margin and outer edge ofsemi-conductor wafer disks.

FIG. 2 is a vertical sectional view through a portion of the apparatusof FIG. 1 to illustrate one specific form of such an apparatus.

FIG. 2a is a partially broken away vertical sectional view through aportion of an apparatus, similar to FIG. 2, to illustrate an alternativespecific form of such an apparatus.

FIG. 3 is a vertical sectional view of the apparatus shown in FIG. 1,taken in a direction which is orthogonal to the direction of the sectionof FIG. 2, and with portions of the apparatus removed for purposes ofillustration.

FIG. 4 is an illustration of a portion of the apparatus of FIG. 1 shownin use to evaluate defects in a single semi-conductor wafer disk.

FIG. 5 illustrates one form of a wafer lifting and rotation apparatususable in the embodiment of FIG. 1 for lifting an individual waferupwardly from a wafer cassette and for rotating the wafer during defecttesting.

FIG. 6 illustrates a top view of one form of a sensor and detectorsupport for supporting a plurality of light sources and light detectors,such as LEDs which emit visible light and detectors of such light.

FIG. 7 is a side elevation view of the support of FIG. 6.

FIG. 8 is an end view of the support of FIG. 6.

FIG. 9 is an end view of the support of FIG. 6 with a wafer edge indiciadetector for detecting a notch or other indicia to indicate a referenceposition on the wafer.

FIG. 10 is a horizontal sectional view taken along line 10—10 of FIG. 7.

FIG. 11 is a vertical sectional view of the support of FIG. 6, takenalong line 11—11 of FIG. 6.

FIG. 12 is a vertical sectional view of the support of FIG. 7, takenalong line 12—12 of FIG. 7.

FIG. 13 is a view like FIG. 11 shown with LEDs and detectors in place,together with a wafer notch detector, and also illustrating a portion ofa semi-conductor wafer (shown in transparent form for convenience, itbeing understood that these wafers are typically optically reflective).

FIG. 14 is a view like FIG. 10 with the LEDs and light detectors shownin place.

FIG. 15 is a view like FIG. 12 with light detectors in place and alsoshowing portions of the outer edge and side edge margins of a wafertoward which the detectors are focused.

FIG. 16 illustrates an exemplary circuit diagram, partially in schematicform, for use with the defect detector of FIG. 1.

FIGS. 16a and 16 b are exemplary circuit diagrams of one form of a lightsource intensity control for use with the defect detector of FIG. 1.

FIG. 17 illustrates a display of a detector output before and afterprocessing to indicate defects.

FIG. 18 is a display in polar form of processed signals from a detector.

FIG. 19 illustrates one form of a visual display indicating the resultsof testing of various wafers in a wafer cassette.

FIGS. 20-24 illustrate a flow chart of an exemplary wafer detectingprocess utilizing the apparatus of FIG. 1 and the circuit of FIG. 16.

FIGS. 25 and 26 illustrate alternative arrangements of light sources anddetectors utilized in an electronic media edge detect detectionapparatus.

FIG. 27 illustrates a top view of another form a sensor and detectorsupport for supporting a plurality of light sources and light detectors,such as LEDs and detectors of light from the LEDs.

FIG. 28 is a side elevation view of the support of FIG. 27.

FIG. 29 is an end view of the support of FIG. 27 with a wafer edgeindicia detector for detecting a notch or other indicia to indicate areference position on the wafer.

FIG. 30 is an vertical sectional view of the support of FIG. 28 takenline 30—30 of FIG. 28.

DETAILED DESCRIPTION

FIG. 1 illustrates one form of a defect detector for testing electronicmedia to determine whether side edge portions and an outer edge of suchmedia contain defects. Although not limited to this specificapplication, the embodiment shown in FIG. 1 is specifically designed fordetermining edge defects in disks such as semi-conductor wafers.

More specifically, the unit 10 includes a housing 12 supported by atable or other support 14. In the embodiment of FIG. 1, a cassette 16 isshown. A cassette is a wafer/disk holding and transporting device thatholds multiple wafers. Cassettes are typically molded with integratedlocating and holding features along with equally spaced guides thatdefine slots within which individual wafers are positioned and heldseparate from one another. Typical cassettes meet certain industrystandards, especially with respect to the location of the first waferand the spacing of subsequent wafers. In one common approach, cassettesoften have an “H” bar, which is a locating device positioned at one endof the cassette and parallel to the first wafer. Two brands of cassettescommon are Fluoroware® and Empak®. The cassette 16 includes a pluralityof wafer holding slots, two of which are indicated by the number 18 inFIG. 1. Wafers 21 are shown positioned within the slots. Although acassette may contain any number of wafers, a common cassette includes 25slots to accommodate up to 25 wafers. The wafers 21 illustrated in FIG.1 are of a circular configuration, although the invention is not limitedto testing electronic media of this specific shape. Cassettes 16 aretypically transported either manually by an operator or by a machine. Inthis case, the cassette is typically supported and transported in theorientation shown in FIG. 1 to prevent the wafers from falling out ofthe slot openings at the top of the cassette. Removal and/or placementof a cassette from or into the unit may be done manually by an operator.For example, an operator may place his or her hands on the sides of thecassette or gripping tabs on the exposed end of the cassette (dependingupon the protocol of the facility), raising the cassette slightly toclear locating features in a cassette support of the unit 10, such as inthe upper surface of an index-and-locate platform 20 included in theunit. For example, such features may include first and second slopedwalls 22, 24 which help guide the cassette into the platform as well aswalls at the end of the platform (one being indicated at 26 in

FIG. 1 and at 27 in FIG. 2) to locate the cassette longitudinally on theplatform. The cassette may also be placed or removed from theindex-and-locate platform 20 by a machine.

As can be seen in FIG. 1, the illustrated cassette 16 has a central opensection 28 through which the wafers may be accessed by a wafer liftingapparatus to raise and lower the individual wafers from the cassetteduring testing. An edge defect sensor assembly 30 is supported by theunit for examining the outer edge and side edge margins of individualwafers when they are indexed into position and raised in proximity tothe sensor assembly for testing. In this specific form, the defectsensor assembly 30 is shown supported on an idler arm 32 which ispivotally coupled to the housing 12. Respective first and secondrotatable guide pulleys or rolls 34, 36, also carried by arm 32, engagethe upper edge of the wafers during the testing procedure.

In the illustrated embodiment with circular disk wafers as theelectronic media, the wafers are raised individually into position fortesting by the sensor assembly 30 and rotated during testing asexplained below. In the event non-disk-like shaped electronic media aretested, a similar sensor assembly may be used with the sensor assemblyand media under test being moved relative to one another to in effectscan the edge of the media for defects utilizing the sensor assembly.

With reference to FIGS. 2 and 3, one of the wafers 21 is shown in anelevated position for testing with the wafer being driven in rotation,in this example, in the direction indicated by arrow 40 (FIG. 2). In theform shown, platform 20 is supported along one side edge by an elongatedslide 42 positioned within a guide rail 44. In addition, the oppositeside of platform 20 is supported by a motorized linear slide indicatedat 46. Slide 46 and rail 44 are carried by respective upright supports48, 50 coupled to the bottom 52 of the housing 12. FIG. 2 illustrates acoordinate system 54 having respective x, y and z axes with, in thiscase, the y-axis extending perpendicularly into the page of FIG. 2.Platform 20 is supported by the slide elements for movement in the ydirection toward and away from the sensor assembly. This motion is alsoshown by the arrow 56 in FIG. 3. In the illustrated embodiment, a motor60 of the motorized linear slide is controlled by a motor controller(which in turn may respond to computer controls as indicated below)moves the cassette 16 in the y direction to advance and index the wafersinto position along the y-axis for testing. As one specific example, they-axis motorized linear slide with matching motor controller may be anIAI® RC-S5L actuator and an RCA-S controller. The cassetteindex-and-locate support or platform 20 holds the cassette 16 in a knownposition when the cassette is positioned by the locating elements of theplatform 20. The slide 42 may comprise a bearing carriage that rides inchannel 44 with the channel being U-shaped as shown. As a specificexample, this assembly may comprise a Rollon® CSW18-100U slider and aULV-18 Series rail.

In the form shown, the center of the index-and-locate platform 20 hasbeen removed to provide access to the opening 28 at the bottom of thecassette. Consequently, the platform 20 may straddle a wafer lifting anddrive mechanism, such as the motorized drive roll assembly indicated at70 in FIG. 2. The illustrated drive motor assembly 70 is designed toraise the wafer being tested upwardly in the cassette such that thewafer no longer contacts the cassette and, in conjunction with rollers34, 36, support the wafer reliably for scanning by the sensor assembly30 for defects. Although mechanism 70 may take other forms, particularlyif the electronic media takes shapes other than being circular, in theform shown the assembly includes a first drive roll 72 supported forrotation about an axis which is parallel to the y direction and a secondspaced apart drive roll 74 supported for rotation about a axis parallelto the axis of rotation of roll 72. The rolls 72, 74 may comprise twoprecision ground V-shaped pulleys or drive rollers which capture androtate the wafer about the center axis 80 of the wafer. Although othermaterials may be used, rolls 72, 74 may be of 70 to 80 durameter shore Apolyurethane. As a result, the lower edge portion of wafer 21 is guidedinto the grooves of these drive rollers when the rollers are lifted intoengagement with the wafer. The drive rollers may be driven by a motor82, such as a DC gear motor, with a Maxon® 2023 Series motor with/gearhead being a specific example. The motor 82 may be coupled to the driverolls by means of a timing belt 86 (FIG. 3) and belt idler pulley 88.The assembly 70 is coupled to the housing 12 for upward and downwardmovement in the z direction. Although other mechanisms may be used, inone specific approach, the assembly 70 is carried by a “Z” axis linearslide for supporting and guiding the movement of the assembly 70upwardly and downwardly. As a specific example, a THK® RSR9 Serieslinear slide/carriage assembly may be used for this purpose. A mechanismis also provided for raising and lowering the drive assembly 70.Although other forms of elevating mechanisms may be used, such as anelectric motor coupled to a drive screw, in the illustrated example apneumatic cylinder 94 is utilized for this purpose. The housing of thecylinder 94 is coupled to the framework for the unit. In addition, thepiston rod 96 of cylinder 94 is positioned to engage the assembly 70such that extension of the cylinder raises the assembly and retractionof the cylinder lowers the assembly in this specific example. As bestseen in FIG. 3, the assembly 70 may include a bracket 100 havingupwardly extending bifurcated or spaced apart leg portions 102, 104which support the respective drive rolls 72, 74. In addition, thebracket 100 may have an outwardly projecting flange portion 106 which iscoupled or connected to the upper end of the rod 96 of cylinder 94.Cylinder 94 is typically designed to raise and lower the drive assemblybetween upper and lower stops (not shown) and thus between respectivewafer drive lifted and wafer drive retracted positions. As a specificexample, cylinder 94 may comprise a Compact® T12X3/4 double acting aircylinder. A directional air valve may be controlled by a computer tothereby control the operation of the air cylinder and the position ofthe assembly 70. For example, a Clippard® E4-1ES-24VDC solenoid valvemay be used for this purpose with air being delivered to one port of thecylinder to extend the piston rod 96 and raise assembly 70 and toanother port of the cylinder to lower the piston rod and retract theassembly.

In the embodiment shown in FIG. 3, first and second sensors 110, 112 areprovided for detecting the position of the drive roll assembly 70 in theraised drive position (sensor 110) and in the lowered retracted position(sensor 112). These sensors provide signals to, for example, a computerfor use in determining the position of the drive assembly. As a specificexample, sensors 110, 112 may be slotted optical sensors such as SUNX®PM-K24 sensors.

FIG. 5 illustrates an enlarged view of the illustrated form of assembly70 and associated components as discussed above. Like elements to thosein FIGS. 2 and 3 have been assigned like numbers in FIG. 5 and will notbe discussed further. In FIG. 5, bracket 100 is shown with a flange 120projecting outwardly to pass between the slots defined by the respectiveslotted sensors 110, 112. Flange 120 interrupts a beam passing between arespective light emitter and detector of the sensors 110, 112 toindicate the positioning of the assembly 70 in the respective raised andlowered positions.

In FIG. 3, the cassette 16 is shown shifted partially to the right inthis figure (in the y direction as indicated by arrow 56) to positionthe first wafer slot of the cassette in position for testing of a wafercontained therein. More specifically, in FIG. 3, the drive mechanism hasbeen raised to lift this first wafer upwardly away from the cassette 16so that it may be rotated without engaging the cassette. This minimizespossible damage to the wafer from rubbing against the cassette as wellas debris being generated by any such rubbing action. When theillustrated cassette 16 is positioned in its initial unload/loadposition (see FIG. 1) through openings through the sides of the platform20 are blocked by the cassette. One such opening 120 in the left side ofplatform 20 is shown in FIG. 3. When in the load/unload position, athrough-beam optical sensor, one portion of which is indicated at 122 inFIG. 3, is in alignment with the opening 120 and the correspondingopening at the opposite side of the platform 20. In other words, whenplatform 20 is shifted to the left in FIG. 3 to the load/unloadposition, an optical beam (e.g., from element 122) passes through theopenings in the sidewall when no cassette is present. When a cassette isproperly positioned in the platform 20 and when the platform is in theunload/load position, the cassette interrupts the optical beam passingbetween element 122 and a corresponding detector at the opposite side ofthe platform. The beam is thus broken to indicate the presence of thecassette. A cassette position indicator is optional (for example, anoperator can visually determine whether the cassette is properlyloaded). Also, other forms of cassette positioners may be utilized.

FIG. 3 also illustrates a cover 130 pivoted at 132 to the housing 12 forpivoting in the direction indicated by arrow 134 between open and closedpositions. A cover position sensor may optionally be used to sense andindicate whether the cover is in a closed position. For example, upondetection of the initial opening of the cover, the apparatus may beturned off to prevent, for example, exposure of a worker to moving partsof the unit. In general, cover 130 (which in this case has a handle 136)shields the sensor and detector assembly 30 from ambient light thatcould interfere with defect detection since the illustrated assembly 30utilizes light sources and light detectors for edge defectdetermination. If ambient lighting conditions are constant and are atrelatively low intensity levels, then shielding by a cover or otherlight shielding mechanisms is not necessary. When cover 130 is opened,sufficient clearance is provided along the sides, top and front of theunit 12 to facilitate ergonomic loading of a cassette 16 onto theplatform 20. One suitable form of cover closed sensor is a SUNX® PM-K24sensor. A power supply, not shown, is included to provide 24-volt DCpower and other power levels to components included in the unit. Housing12 contains brackets and framework, such as shown in these figures, tosupport the various components and sensors therein.

With reference to FIG. 2, although variable, a typical speed of rotationof the wafer 21 being tested is 2 seconds per revolution.

As previously mentioned and with reference to FIG. 2, idler arm 32supports the illustrated sensor assembly 30. The illustrated sensorassembly includes a sensor support 152 which may take the form of asensor support block 156 as shown in FIG. 6. In this specific example,three threaded bores 158, 160 and 162 are provided at the upper surface169 of block 156. Bores 160, 162 being adjacent to a first end 164 ofthe block while bore 158 is adjacent to the opposite end 166 of theblock. As can be seen in FIG. 6, these bores provide a three-point mountfor the block 156 to the idler arm 32. More specifically, threealignment screws may be captured in idler arm 132 with the screw headsbeing exposed from above. These alignment screws are threaded into therespective bores 158, 160 and 162. By tightening and loosening thesescrews (two of which are indicated at 170 and 172 in FIG. 4), the sensorblock elevation may be adjusted to position light emitters and detectorssupported by the sensor block at the proper elevation for focusing onthe desired side edge margins and outer edge of the wafer 21 beingtested. The block 156 also has side surfaces 167, 171 and a bottomsurface 165. Rolls 34, 36 are typically idler rolls and may beidentically configured to rolls 72 and 74. For example, rolls 34, 36 maybe “V” grooved idler rolls of a suitable material such as 70-80durameter shore A polyurethane, with other materials also beingpossible. The V-groove of these rolls capture the outer edge of thewafer 21 and guide the wafer through the sensing centerline of the edgedefect sensor assembly 30 as the wafer is rotated.

Idler arm 32 is typically pivoted to permit the idler arm to moveupwardly and downwardly. For example, arm 32 may be pivoted to a pivotsupport such as a pivot alignment block 160 (FIG. 2) for pivoting aboutan idler arm pivot axis 162. Support 160 is carried by a support, suchas a block 164 positioned at the upper end of an upright idler armsupport post 166. Block 164 is typically rigidly connected to supportpost 166 and provided with elongated slots extending primarily in the xdirection. Pivot alignment block 160 is bolted to support 164 with thebolts extending through the slots. When the mounting bolts are loosened,pivot alignment block 160 may be moved in the x direction to alignpulleys 34, 36 with pulleys 72, 74 to provide a four point contact withthe wafer 21. The wafer 21 is centered by the pulleys 34, 36 at thedesired distance (e.g., equal distance) between sensors focusing on theside edges of the wafer. The bolts are then tightened to securely mountpivot alignment block 160 to support 164. A stop 170 carried by theupper end of a shaft 172 which extends through idler arm 32 limits thedownward motion of the sensor assembly support portion of the idler arm.The stop 170 prevents the idler arm from lowering below a minimumacceptable position in this example. The idler arm is counterbalanced byincreasing the weight of the portion of the idler arm 174 to the left ofpivot 162 in FIG. 2. For example, although variable, the idler armassembly may be counterbalanced so that approximately 20 grams pressureis applied by rolls 34, 36 to the edge of the wafer 21. Movement of theidler arm 32 may also be limited or damped by a damping mechanism suchas a damping cylinder 176. As shown in FIG. 2, in this example the rod178 of cylinder 176 is coupled to the idler arm 32 at the left side ofpivot 162 in this figure. The cylinder housing 180 of cylinder 176 ismounted by a bracket 182 to the support post 166. Although variable, asa more specific example, the damping coefficient of damping cylinder 176may be 0.2 pounds per inch per second. As a specific example, thedamping cylinder may be an AIRPOT® S95 Series cylinder. The dampingcylinder facilitates low idler roll contact pressure with the edge ofthe wafer being tested while minimizing any bounce in the idler arm thatmay otherwise be caused by a defect or wafer notch passing in contactwith the various wafer supporting rolls.

FIG. 2a illustrates an alternative form of support for the idler arm 32.In FIG. 2a, components in common with those in FIG. 2 have been assignedlike numbers for convenience. In FIG. 2a, the idler arm 32 is supportedby a mechanism which facilitates adjustment of the position of the idlerarm in x and y directions (see reference coordinate system 54). Inaddition, a mechanism is also provided to permit rotation of the idlerarm about the z axis to facilitate alignment of the upper rollers 34,36with the drive rollers 72,74 (FIG. 2). In FIG. 2a, one form of the x,yadjustment mechanism is indicated generally at 184 and one form of thez-axis rotation adjustment mechanism is indicated generally at 186. Ingeneral, idler arm support 160 is slidably mounted to a base 188 formovement relative to base 188 in both directions along the x-axis withinthe mechanical limits of the system. An adjustment knob 190 is rotatablerelative to support 188 to rotate a drive screw or other base movementmechanism in respective directions to shift platform 160 in the x and −xdirections. A set screw 191 may be used to selectively fix the positionof support 160 in the desired x position of adjustment. A lower portionof x-position base 188, indicated at 192 in FIG. 2a, may be slidablycoupled to a y-position adjustment base 193 such that portion 192 ismovable relative to base 193 in the y-direction within the mechanicallimits of the adjustment mechanism. An adjustment knob 194 rotatablycoupled to y-position base 193 may be rotated in respective oppositedirections to drive, for example, a drive screw to shift component 192and thus the idler arm 32 in the y-directions. A set screw 195 may beused to selectively fix the idler arm in the desired y-position ofadjustment. Member 193 is supported by a pivot platform 196 which isrotatable in opposite directions about the z-axis within limits of thesystem. An adjustment knob 197 drives a rotation drive mechanism, suchas a worm gear, coupled to pivot platform 196 to rotate the platform inthe desired direction. A pin 198 may be inserted into respectiveapertures of member 196 to selectively retain the z-axis adjustmentmechanism at its desired position of adjustment. The x,y and z-axisadjustment mechanisms 184,186 are typically carried by the post 166. Oneform of suitable x-y adjustment mechanism is a Model K55-020 x-y-axismetric stages which is commercially available from Edmond ScientificCompany. A specific example of a suitable z-axis adjustment mechanism isa Model K55-029 metric rotary stages which is also commerciallyavailable from Edmond Scientific Company. Of course, other x,y and zadjustment mechanisms may be used if desired and such mechanisms may beeliminated although this would be less desirable.

In accordance with an optional feature of one embodiment of an edgedefect detector, an optional cleaning system is desirably employed toclean the edge of the wafer prior to moving the wafer relative to one ormore emitters and detectors. Although such a cleaning system may take avariety of forms, in one specific example, a gas cleaning system such asindicated generally at 181 in FIG. 2a may be employed. Cleaning system181 comprises a gas nozzle 183 for directing air toward the edge of thewafer 21. Nozzle 183 is located upstream of the sensor assembly 30. Gasfrom a pressurized source of gas 185, such as nitrogen gas, anotherinert gas, or clean dry air, is coupled to nozzle 183 through a valve187 and a flow regulator 189. Valve 187 may open in response to acontrol signal on a line 201 to permit the passage of pressurized gasfrom the source to the nozzle. Flow regulator 189 provides a mechanismfor adjusting the volume of gas flow and may be used to shut off the gasflow in the event gas bathing of the wafer is not desired. Typically,the control signal 201 is generated in response to raising the assembly70 (FIG. 3) and lifting of the wafer 21 into position for examination.The computer may cause the generation of the control signal at input 201when the drive roll assembly 70 is detected in the raised drive position(e.g., by sensor 110).

With reference to FIG. 4, which shows a slightly different configurationfor the drive rolls 72, 74 and motor 60, one exemplary layout for aspecific embodiment in accordance with the present invention isillustrated, it being understood that other configurations may be used.In this specific example, the wafer 21 has a position indicia which canbe detected to locate a known position on the wafer. This positionindicia may be added prior to testing of the wafer or may be formedduring wafer manufacture. In the embodiment shown in FIG. 4, the indiciacomprises a notch 200. The axis of rotation of pulley 74 is indicated at202 in FIG. 4. In addition, the axis of rotation of pulley 72 isindicated at 204. Furthermore, the axis of rotation of pulley 34 isindicated at 206 while the axis of rotation of pulley 36 is indicated at208. In addition, the illustrated sensor assembly 30 includes an indiciadetector 210 which in this case comprises a detector for detecting thepassage of notch 200. In one specific form, detector 210 comprises athrough-beam slotted sensor which is positioned such that an opticalbeam is broken by the wafer except when the notch passes through thesensor. As a specific example, notch detector 210 may comprise an SUNX®PMK24 sensor. Notch detector 210 is carried by block 156 at the leadingedge of the block, in this example, such that notch 200 passes throughdetector 210 prior to passing defect sensors carried by block 156. Thelocation of the through beam of this detector 210 is indicated at 214 inFIG. 4.

The block 156 may be machined, molded or otherwise formed to hold aplurality of light emitters, such as Chicago Miniature Lamp, Inc.® No.CMD204UWC emitters or LEDs and a plurality of light detectors (such asTAOS® No. TSL256 detectors). Although fewer or more emitters anddetectors may be used than shown in FIG. 4, in the illustrated assembly,two sets of emitters and detectors are provided. The first set isindicated generally at 220 in FIG. 4 while the second set is indicatedgenerally at 222 in this figure. The first set includes six lightemitters, two facing the front side edge margin of the wafer, two facingthe back side edge margin of the wafer, and two facing the outer edge ofthe wafer. The first set 220 also includes three detectors with thefirst being positioned to receive light scattered by defects at thefront side edge margin of the wafer, the second being positioned toreceive light scattered by defects from the back side edge margin of thewafer and the third being positioned to received light scattered bydefects from the outer edge of the wafer to a distance of about 2 mmtoward the center of the wafer. The front and rear facing detectorsreceive scattered light from a wider portion of the side margin of thewafer edge. The respective detectors are focused on specific focalpoints. The associated two emitters for each detector in this specificexample have light energy directed at an angle toward the focal pointsof the respective detectors. In this example, the absence of a defect,light from the emitters is reflected from the wafer generally in adirection away from the associated detector. In contrast, uponencountering a defect, the light is scattered with some of the lightbeing detected by the associated detector and with the amount ofdetected light and variations in the detected light being usable todetermine the presence of a defect as explained in greater detail below.The location of the focal points of the sets of emitters and detectors220, 222 in this example are along radial lines 230, 234 in FIG. 4. Inaddition, the axis 206 of wheel 34 is along radial line 236, the focalpoint of detector 210 is along radial line 238; the axis 208 of pulley36 is along radial line 240; the axis of pulley 74 is along radial line242; the axis 204 of pulley 72 is along radial line 244; the leadingedge of notch 200 is along radial line 246; and the trailing edge ofnotch 200 is along radial line 248. Radial lines 250, 252 are positionedon opposite sides of the respective lines 248, 246 and indicate aportion of the wafer edge that is ignored, in this example, to eliminatedistortions caused by notch 200 passing by the respective light emittersand detectors. Obviously the notch 200 rotates as the wafer is driven inrotation.

In this specific example, the angle A between lines 246 and 248 is 2.26degrees; the angle B between lines 250, 252 is 3.42 degrees; the angle Cbetween lines 238, 242 is 151.57 degrees; the angle D between lines 238and 244 is 178.95 degrees; the angle E between lines 236 and 238 is40.75 degrees; the angle F between lines 234 and 236 is 20.56 degrees;the angle G between lines 230 and 238 is 9.29 degrees; the angle Hbetween lines 238 and 240 is 11.27 degrees; the angle I between lines230 and 234 is 10.89 degrees; and the angle J between lines 230 and 240is 20.56 degrees. Again, these angles and positions may be varied butprovide a suitable example of an edge detector in accordance with onespecific embodiment of the present invention.

Referring again to FIG. 2, upon energizing the solenoid valve whichcontrols air flow to cylinder 94, pressurized air is delivered to anappropriate input on the air cylinder to extend piston rod 96 and raisethe drive roll assembly 70 upwardly in a z direction. The V-grooveddrive rolls 72, 74 engage and center the semi-conductor wafer 21 both inthe groove of the rolls and between the rolls while raising the wafer inthe z direction. The wafer is raised approximately 9 mm to clear thecassette in this specific example. Before the wafer is raised to itsmaximum elevation by assembly 70 in the z direction, the wafer entersand is centered by the V-grooves of the two idler rolls 34, 36 which inturn position the edge of the wafer in the sensing centerline of theedge defect sensor assembly 30. This z-axis upward movement of the wafer21 also raises the idler arm assembly approximately 1 mm, resulting inthe application of a light force to the edge of the wafer. At themaximum raised position, both the drive rolls 72, 74 and the idler rolls74, 36 combine to make a near perfect 4-point contact with the outermostedge of the wafer while positioning the wafer edge in the correctlocation for measurement by the edge defect sensor assembly 30. This4-point wafer contact virtually eliminates any wafer bounce that couldotherwise occur when the wafer notch 200 contacts an idler or drive rollif a 3-point contact system were used. However, a 3-point or othercontact system could be used, although less desirable. Other wafersupporting mechanisms may also be used. Also, although less desirable,the wafer could be rotated without lifting the wafer from the cassette.The grooved idler and drive rollers provide self-centering and alignmentof the wafer being tested. In addition, this method of supporting thewafer during testing substantially eliminates contact with the front orback sides of the wafer. In addition, in the illustrated approach, nocontact occurs between the wafer cassette and wafer during testing ofeach individual wafer. Moreover, the wafers need not be removed from thecassette slots during testing. However, in an alternative embodiment,wafers may be tested individually without a cassette. For example, thewafers may simply be placed on the drive rolls (for example utilizing avacuum wand), raised into position and then tested. As is also apparentfrom FIG. 1, when cassettes are used, they may be placed directly ontothe apparatus without the need to be rotated by an operator or anothermechanism prior to placement in the apparatus for subsequent testing.

Although not required, redundant sensors such as sets 220, 222 may beprovided for front, back and top edge wafer defect detection. Forexample, the focal points of the sensors may be offset from the center80 of the wafer so as to direct light and detect light toward the waferat different angles. For example, four angles of emitter emission may beprovided along the front edge margin of the wafer, along the back edgemargin of the wafer, and along the top edge of the wafer. Multipleangles of emitter emission increases the ability of the system to detectminute defects. In addition, the use of redundant sensors and emittersallows for the removal of anomalies that may be caused, for example, bythe wafer notch touching one of the idler or drive rolls. For example,the system will know when a notch passes a roller and thus can ignorereadings for a particular location along the wafer from a first set ofsensors at this time. Data for this position along the wafer may then beread by the second set of sensors when the notch is no longer engaging adrive idler roll. This data can then be inserted into the data stream inplace of the ignored data that would have been gathered by the first setof sensors at a time when the notch is engaging one of the rolls.

Yet another form of sensor support 152 may be used, such as the sensorsupport block illustrated in FIGS. 27-30. These figures correspond toFIGS. 6, 7, 9 and 12. Common components in these respective figures havebeen assigned the same number for convenience and will not be discussedfurther.

In FIGS. 27-30, the respective upper comers of the support 152 of theFIGS. 6 and 7 form have been removed to produce respective first andsecond beveled surfaces 460,462. Surface 460 extends between sidesurface 167 and top surface 169 while surface 462 extends between sidesurface 171 and the top surface. Although not limited to a particularangle, desirably the surfaces 460,462 are at a 45 degree angle withrespect to horizontal, such as relative to the top surface 169 if itconstitutes a horizontal surface. A light detector receiving bore 464extends from groove 300 adjacent to surface 460 to the groove 260 andcommunicates with the groove 260 through an opening 466 which, as can beseen in FIG. 30, is midway between the openings leading from therespective bores 304,320 to the groove 260. Similarly, a bore 470extends from groove 300 adjacent surface 462 to the groove 260 andcommunicates with the groove 260 through an opening 472 positionedmidway between the openings leading from bores 304 and 324 to the groove260. The longitudinal axes of bores 464,470 are aligned with respectivefocal points at the respective upper side edge margin portions of thewafer 21 (see FIG. 30). The angles maybe varied and are typicallyselected to provide multiple angles of attack of light toward the edgemargin of the wafer being tested to minimize the possibility of missingdefects. Similarly, a detector receiving bore 472 extends from groove302 adjacent surface 460 to the groove 260. In addition, a detectorreceiving bore 480 extends from a location adjacent surface 462 and ingroove 302 to the groove 260. Bores 474,480 may be aligned in the samemanner as bores 464,470 although their longitudinal axes would bealigned with respective focal points at opposite upper side edge marginportions of the wafer 21 which differ from the focal point of the axesof bores 464,470.

A set of light source receiving bores 482,484 extend inwardly fromsurface 460 to the groove 260 and communicate with the groove 260through respective openings. The longitudinal axes of bores 482,484 andof bore 472 intersect at a common focal point. A set of bores 486,488extend inwardly from surface 460 and communicate with groove 260 throughrespective openings. The longitudinal axes of bores 486,488 and of bore464 intersect at a common focal point. In addition, a set of bores490,492 extend from surface 462 and communicate through respectiveopenings with the groove 260. The longitudinal axes of bores 490,492 andof bore 480 intersect at a common focal point. Also, a set of bores 494,496 extend from surface 462 and communicate with groove 260 throughrespective openings. The longitudinal axes of bores 494,496 and of bore470 intersect at a common focal point. Thus, FIGS. 27-30 illustrate asupport with additional sets of respective light delivery bores andassociated light detection bores.

The diameter of the bores of the sensor support blocks may vary and theyare not required to be the same. However, a typical diameter is 0.063inch. All or selected bores, for example those associated with thedetectors, may be roughened or textured to minimize light at other thanthe angles of interest being reflected along the walls of the bores. Inone form of texturing, the bores are tapped to form threads in the borewalls. Threads at a pitch of 0.4 mm which are deep enough to remove theotherwise flat surfaces of the bores are a specific illustrativeexample. This texturizing reduces the amount of spurious light thattravels to the detectors.

The damping mechanism, such as the damping cylinder 176, attached to thesensor assembly supporting arm 32 enables very light idler roll contactwith the wafer edge while minimizing the possible bouncing of the idlerarm 32.

Thus, in the embodiment described above positive detection of the wafernotch is accomplished utilizing a slotted optical sensor. In addition,the illustrated system does not require the total removal of wafers froma wafer holding cassette for separate inspection and as a resultfacilitates a higher throughput of inspected wafers.

Although other energy sources such as lasers, light sources that aresplit or otherwise divided into plural light sources and ultrasonicemitters or sensors may be used, the embodiment described abovedesirably may utilize inexpensive visible light emitters and inexpensivelight to voltage/current converters. This simplifies the electronicsinvolved in the system and also reduces the costs of the system. Forexample, as explained below, the electronics may consist of 3 resistors,3 manually adjusted or digitally adjusted potentiometers for controllingemitter intensity and an off-the-shelf analog to digital card whichplugs into any standard PC to provide data from the light detectors in aform usable for processing by the computer.

The illustrated form of sensor support 152 and sensor assembly 30 isbest seen with reference to FIGS. 6-15. In the illustrated form, sensorsupport 152 comprises the sensor support block 156 which is providedwith a longitudinally extending groove extending inwardly into the block156 from the bottom surface 165 of the block, this groove beingindicated at 260 in some of these figures. As can be seen in FIG. 9, thenotch detector 210 has a slot 262 which is aligned with groove 260 whennotch detector 210 is mounted, such as by screws, to the end 166 ofblock 152. The centerline of slot 262 and of groove 210 is indicated at264 in FIG. 9. As can be seen in FIGS. 6, 11 and 13, the illustratedblock 156 includes a first set of bores 270, 272 and a second set ofbores 274, 276. These bores communicate from the upper surface 169 ofblock 156 to the groove 260. More specifically, the bores 270, 272, 274and 276 communicate with the groove 260 through respective openings 280,282, 284, and 286. The longitudinal axes of bores 270, 272 intersect ata focal point location 290 as explained below. In addition, thelongitudinal axes of bores 274, 276 intersect at a focal point 292.Although variable, the angles between the longitudinal axis of bore 270and bore 272 may be sixty degrees and the angle between the longitudinalaxis of bore 274 and bore 276 may also be sixty degrees.

As best seen in FIGS. 6, 7, and 12, spaced apart grooves 300, 302 may beprovided in block 156. Each of these grooves may extend from a locationadjacent to, but spaced from, the lower surface 165 of block 156, alongthe side surface 167 of the block, across the top surface 169 of theblock and downwardly along the opposite side surface 171 of the block toa location adjacent to, but spaced from, the lower surface 165. A bore304 extends from groove 300 to the groove 260 and communicates withgroove 260 through an opening 305 which, as can be seen in FIG. 11, ismidway between openings 284 and 286. Similarly, a bore 306 extends fromgroove 302 to groove 260 and communicates with groove 260 through anopening 308 positioned midway between the openings 280 and 282. Thelongitudinal axis of bore 306 is aligned with the focal point 290.Similarly, the longitudinal axis of bore 304 is aligned with focal point292. It should be noted that the angle between the longitudinal axes ofbores 274, 276 may be the same as the angle between the longitudinalaxes of bores 270, 272 or the angles may differ. The angles aretypically selected to provide multiple angles of attack of light towardthe edge of the wafer being tested to minimize the possibility ofmissing defects.

As also can be seen from FIG. 12, a bore 320 extends inwardly into theblock 156 from groove 300 at side surface 167 and communicates withgroove 260 through an opening 322. In like manner, a bore 324 extendsinwardly from groove 300 at side surface 171 and communicates withgroove 260 through an opening 326. Bores 320, 326 are also shown in FIG.10. Bores 324 and 320 have longitudinal axes which are spaced ninetydegrees from the longitudinal axis of bore 304. In the same manner abore 330 extends inwardly from groove 302 and surface 171 to groove 260with bore 330 communicating with groove 260 through an opening 332. Abore 334 extends inwardly from groove 302 and surface 167 to groove 260and communicates with groove 260 through an opening 336. A first set ofbores 340, 342 extend inwardly from surface 167 to groove 260 andcommunicate with the groove 260 through respective openings 344, 346.The longitudinal axes of bores 340, 342 and of bore 334 intersect at afocal point 350. A set of bores 352, 354 extend inwardly from surface171 and communicate with groove 260 through respective openings 356,358. The longitudinal axes of bores 352, 354 and 330 intersect at afocal point 360. In addition, a set of bores 370, 372 extend inwardlyfrom surface 167 and communicate through respective openings 374, 376with the groove 260. The longitudinal axes of bores 370, 372 and bore320 intersect at a focal point 378. In addition, bores 380, 382 extendfrom surface 171 inwardly and communicate with groove 260 throughrespective openings 384, 386. The longitudinal axis of bores 380, 382and of bore 324 intersect at a focal point 388. The angles betweenrespective bores 340, 342; 352, 354; 370, 372; and 380, 382 may be thesame as the angles between respective sets of bores 270, 272 and 274,276. Alternatively, the angles may be varied. In addition, additionalbores may be provided to accommodate additional light emitters anddetectors at other angles of attack for further refinement of the waferedge defect detection.

With reference to FIG. 13, the illustrated set 220 of light emitters anddetectors include first and second light emitters 400, 402 positionedwithin respective bores 270, 272 and a light detector 404 positionedwithin bore 306 for detecting light scattered from the outermost edge ofwafer 21 upon the occurrence of a defect. Light emitters 400, 402 anddetector 404 are focused on focal point 290. In the absence of a defect,light from emitters 400, 402 is substantially reflected away fromdetector 404.

The set 220 also includes light emitters 410, 412 (FIG. 14) positionedin respective bores 340, 342 and a light detector 414 positioned withinbore 334. Emitters 410, 412 and detector 414 are directed toward focalpoint 350 along a first side edge margin of the wafer 21. In addition,the set 220 includes light emitters 416, 418 positioned in respectivebores 352, 354 and a light detector 420 positioned within bore 330.Emitters 416, 418 and detector 420 are directed toward focal point 360and thus inspect the opposite side edge margin of the wafer from theside edge margin inspected by emitters 410, 412 and detector 414. Theset 222 of emitters and detectors includes a first light emitter 430positioned within bore 274, a second light emitter 434 positioned withinbore 276 and a light detector 436 positioned within bore 304. Lightemitters 430, 434 and light detector 436 focus on focal point 292. Theset 222 in this embodiment also include light emitters 438, 440positioned within respective bores 370, 372 and a light detector 442positioned within the bore 320. Light emitters 438, 440 and lightdetector 442 are focused on focal point 378 (FIG. 14). In addition, theset 222 includes light emitters 444, 446 positioned within respectivebores 380, 382 and a light detector 448 positioned within the bore 324.The light emitters 444, 446 and light detector 448 are focused on focalpoint 388.

In the sensor and detector support embodiment depicted in FIGS. 27-30,light emitters (not shown) may be positioned in respective bores 482,484and a light detector (not shown) positioned within bore 472. Theseemitters and detectors are directed toward a respective focal pointalong a first side edge margin of wafer 21. Additional light emitters(not shown) may be positioned in respective bores 486,488 and a lightdetector (not shown) positioned within bore 464. These emitters anddetectors are directed toward a different focal point at the first sideof the wafer and thus are used to inspect another portion of the firstside edge margin of the wafer. Also, light emitters may be positioned inthe respective bores 490,492 and an associated detector may bepositioned in bore 480. These emitters and detectors are directed towardyet another focal point, in this case, at the opposite side of waferfrom the detector positioned in bore 472. In addition, light emittersmay be positioned respectively in bores 494,496 and a light detector maybe positioned in bore 470. This detector and these light emitters arefocused on an additional focal point located at the second side of thewafer opposite to the focal point to which the detector in bore 464 isdirected. With this construction, the emitters in bores 488,486 and494,496 as well as the detectors in respective bores 464,470 thusconstitute additional light emitters and detectors in the first set 220of light emitters and detectors. In addition, the light emitters inrespective bores 482,484 and 490,492 together with the light detectorsin respective bores 472 and 480 comprise additional emitters anddetectors of the second set 222 of light emitters and detectors.

FIG. 15 illustrates the focusing of light detector 442 on one side edgemargin of wafer 21; the focusing of light detector 448 on the oppositeside edge margin of wafer 21; and the focusing of detector 436 on theouter edge of wafer 21.

Again, the numbers and locations of the various detectors and emittersmay be varied. Although other supports may be used for supporting thedesired emitters and detectors, a machined or molded block 156 isextremely reliable and can be readily manufactured.

FIG. 16 illustrates one form of circuit schematic diagram and associatedcomponents which may be used in connection with the embodiment describedabove.

The output of the exemplary light detectors may, for example, range from0 to 4.5 volts. In a specific example, it is desirable to adjust thisoutput to be somewhere in the mid-range when no defect is beingdetected, for example from about 2 to 2.5 volts. In the illustratedembodiment, respective potentiometers 500, 502, 504 may be adjusted toadjust the output of the light emitting diodes along the front side, topside and rear side of the sensor assembly 30. Potentiometers 500, 502and 504 may be manually adjusted or may comprise digitally controlledpotentiometers. One way of calibrating the system is to run a testutilizing a wafer which is known to contain no defects. The system canthen be adjusted such that the detectors produce an output in thedesired range. The outputs of the detectors 404, 414, 420, 436, 442 and448 as well as of the notch detector 210 may be fed to an analog todigital card (A/D) 506 which may be plugged into a conventional computersuch as a personal computer indicated at 508.

As an option, another form of a mechanism for automatically orsemi-automatically adjusting light intensity from the light emitters maybe employed. This may be used to compensate for variations in wafersurface reflectivities arising from wafer manufacturing processes. Forexample, the front and rear surfaces of a wafer may have differentreflectivities. Light emitter intensity adjustment may be performed onone or more of the wafers in the cassette, for example on the firstwafer in each cassette or all wafers in each cassette.

In the exemplary form of intensity adjustment mechanism shown in FIGS.16a and 16 b, for example, one of eight intensities is selected forgroups of one or more detectors and their associated emitters. Forexample, the emitters and detectors focused on the same general edgemargin portion of the wafer may be grouped together as the waferreflectivity for these groups is expected to be the same. As a specificexample, for the support 152 shown in FIG. 28, the emitters anddetectors associated with surface 167 may be grouped together, thoseassociated with surface 460 may be grouped together, those associatedwith surface 169 may be grouped together, those associated with surface462 may be grouped together and those associated with surface 171 may begrouped together. Other groupings may be used. Also, the intensity ofindividual emitters or those emitters associated with a particulardetector may be independently adjusted.

In FIGS. 16a and 16 b, an exemplary circuit is shown for adjusting theintensity of several detectors and their associated emitters. This samecircuit may be used for other emitter detector groupings for whichintensity control is desired. A wafer (e.g., the first wafer in acassette) is positioned for examination. The outputs of detectors fromthe group of emitters and detectors which are to be intensity adjustedare monitored. In this exemplary case, the illustrated group consists ofemitters and detectors positioned in bores at surface 167 of the support152 (see FIGS. 10 and 14). That is, the group consists of detector 414and respective associated emitters 410,412 (which are the source oflight detected by detector 414) and detector 442 and respectiveassociated emitters 438,440 (which are the source of light detected bydetector 442).

More specifically, in one example, one of a plurality of adjustments isselected, such as one of eight current values is selected by turning ona selected combination of paralleled transisters Q₁ and Q₂ and Q₃ inresponse to latch output signals from computer 508 to a latch 511. Thelevels correspond to Q₁ and Q₂ and Q₃ (off the circuit path then beingthrough resistor R₄); Q₁ on with Q₂ and Q₃ off; Q₂ on with Q₁ and Q₃off; Q₃ on with Q₁ and Q₂ off; Q₁ and Q₂ on with Q₃ off; Q₁ and Q₃ onwith Q₂ off; Q₂ and Q₃ on with Q₁ off; and Q₁, Q₂, and Q₃ all being on.

The computer 508 may include a display 510, such as a monitor. Inaddition, the computer 508 may include a data entry device which maytake any convenient form. For example, the data entry device may be oneor more of a touch screen, a keyboard 512 and/or a mouse 514.Peripherals such as a printer 514 and a hard drive 516 containingadditional memory for data storage may be included in a conventionalmanner. Computer 508 may also be loaded with a conventional operatingsystem. Data from the light detectors and the notch detector may beperiodically sampled and stored under the control of computer 508. Oneor more input/output cards (I/O cards) may be utilized in the system.The A/D and I/O card functions may be provided in the same card or cardswith a National Instruments® No. 6034E card being one such example. Aschematically represented I/O card is indicated at 520 in FIG. 16. Card520 converts control signals from computer 508 into a form suitable forvarious components under the control of the computer and also convertssignals from the components of the system to a form suitable forprocessing by the computer. The components under computer control mayinclude a y-axis controller 530 to control the y-axis motor 60 (FIG. 3)to cause the wafer cassette to index to desired wafer slots and toreturn to the load/unload position at desired times. The output fromcassette presence sensor 532 is also monitored by the computer todetermine whether a cassette is present in the system when the system inthe load/unload position. For example, in the embodiment of FIG. 3,element 122 is one component of an exemplary presence detector. In theevent a door 130 (FIG. 3) is used, a door closed sensor 534 may producean output which is monitored by the computer to determine whether thedoor 130 is closed and to also determine when opening of the doorcommences.

In addition, the computer 508 may be coupled to wafer lifter raised andlowered position sensors 110, 112 (FIG. 3) for purposes of monitoringwhether the wafer lifter assembly 70 is raised or lowered. Computer 508may also control the mechanism used to raise and lower the wafer lifterassembly 70. Thus, one embodiment, the computer may control a valve 536which causes the cylinder 94 (FIG. 3) to raise and lower the waferlifter. In addition, computer 508 may control the drive motor 82 (FIG.3) used to drive rolls 72, 74 and rotate the wafer which is to beinspected. An optional encoder 540 may provide feedback to the computeron the position of drive motor 82 which can be used by the computer todetermine the position along the wafer where defects are detected. Thisalso allows accurate positioning of the wafer in a cassette followingtesting. As a specific example, the wafer may be rotated to position thewafer notch at a desired position such as the 12 o'clock or verticalposition following testing. In this case, each wafer can be positionedin a similar manner to facilitate downstream processing of the wafers.Alternatively, the wafers may be rotated to position specific detecteddefects at a given position, such as the 12 o'clock position tofacilitate further inspection of these defects. A conventional cameraand controller, indicated at 544, may also be controlled by thecomputer. More than one camera may be utilized if desired. Thus, forexample, once defects have been determined to exist in a wafer, thewafer may be positioned by the computer (e.g., by rotation of the waferto position the defect at a known position to, for example, correspondwith the focus of the camera), such that the camera can be utilized toremotely inspect the defects to determine whether they are indeedsignificant. A camera or optical character recognition (OCR) visionsystem may be used in connection with scanning and entering bar code orother indicia which identifies the particular cassette which carries thewafers being examined. Other cassette ID determining systems may also beused. Such systems, although not required, can be used to track thecassette location throughout the wafer production and evaluationprocess. Also, a conventional vacuum wand and controller indicated at546 may be controlled by the computer to grasp and remove a waferdetermined to have defects. In this case, the housing 12 (FIG. 3) may bemodified to permit the operation of such a wand within the housing. Inaddition, a second cassette may be included in the housing for receivingdefective wafers. The defective wafers may be oriented again in a knownposition prior to delivery to the separate cassette. In this way, thedefective wafers may be separated for subsequent visual inspection ifdesired with wafers passing the inspection remaining in the originalcassette where they can be transferred for downstream processing.

As one specific processing approach, as the wafer edge and detectors aremoved relative to one another, such as by rotation of the wafer, thewafer is monitored to determine the presence of a position indicia suchas a notch. Following the occurrence of the first notch present signal(as determined from signals from notch detector 210) all of the lightdetectors (e.g., the edge defect light detectors and notch sensor) aretypically read as simultaneously as possible and at a sufficiently highsample rate (such as 1000 samples per second) to detect fluctuations indetector outputs caused by edge defects. Sensor sampling may be stoppedupon receiving the second notch present signal corresponding to one fullrotation of the wafer. The tests may be repeated for additionalrotations and the results averaged or otherwise combined if desired. Ifonly a portion of the wafer edge is to be sampled, sampling can stop ata different time. The number of actual samples taken in one waferrotation is then determined. In this example, the voltage samples fromthe notch detector are examined for the first transition from a highvalue (e.g., over 2.5 volts) to a lower value (e.g., under 2.5 volts) todetermine the first detection of the notch. The notch voltage samplesare then searched for the second transition from a high value to a lowvalue to indicate the second detection of the notch. The number ofsamples between the first and second notch transitions is the number ofsamples in one rotation.

The light detector output samples are then analyzed for the purposes ofdetermining the presence of edge defects. Such defects show up as spikesin the voltage values. Although other analytical approaches may be used,in one specific approach, adjacent samples are compared with differencesgreater than a threshold value being noted. More specifically, the firstdifferential of the output voltage sample values may be determined. Thedefect threshold may be adjustable, e.g., by input to the computer, tocontrol the sensitivity of the system. Adjustments may be made, forexample, to accommodate testing of different types of electronic mediaand/or wafer samples and also in accordance with the protocol of theparticular manufacturing plant. The threshold may be establishedempirically. As one way of establishing a defect threshold, one can runtests of a non-defective wafer or other electronic media and also of adefect-containing wafer. The threshold can then be adjusted until thedefective wafer or media is identified without identifying the goodwafer or media as being defective. A default threshold may beestablished by the software program and may be the same or different forvarious media types. Typically the comparison operation begins a givennumber of samples after the first high-to-low transition of the notchsensor signal. In this way, the analysis starts after the notch haspassed the wafer edge defect determining detectors. The comparisonoperation is typically stopped a given number of samples after thesecond high-to-low transition of the notch sensor signal. This stops theanalysis before the notch returns to the edge defect detecting sensors.For example, with reference to FIG. 4, samples between lines 250 and 252may be ignored as this corresponds to a notch edge exclusion zone.

The results of the evaluation of a particular wafer may be stored forsubsequent display or may be displayed as they are being generated. Thedisplay may take any of a number of forms. FIG. 17 shows a screen shotof a computer monitor 510 illustrating exemplary test results. The linelabeled 550 is the output of one of the light detectors. The lineindicated at 552 is the first derivative of the samples displayed online 550. The first detection of the notch occurred generally atlocation 554 along the x-axis. The second detection of the notchoccurred generally at 556. A defect in the wafer is indicated to haveoccurred at location 558 along the x-axis. Although less clear, thisdefect can be seen at the same location along wave form 550. Dependingupon where the threshold is established, the defect at 558 will beindicated. Criteria may be established for determining whetherparticular wafers pass or fail depending for example on the number andmagnitude of the differences that are found, which correspond to thenumber and significance of the defects. With reference to FIG. 18, for agiven wafer the difference data can be plotted in polar graph form. Thisyields a circle with spikes indicating the location of the defectsrelative to the notch. In the graph of FIG. 18, the position of thenotch is indicated at 560 and the position of a defect is indicated at562. This display can be visually presented when, for example theoperator designates a wafer that the operator wants to review for theexistence of possible defects in the wafer. A threshold circle may alsobe included in FIG. 18 to help the operator determine whether asignificant defect has been determined. The difference data from thevarious detectors corresponding to the wafer front edge margin, outeredge and rear edge margin sensors may be displayed together, in variouscombinations, or individually.

FIG. 19 discloses another optional form of display. In FIG. 19, a visualrepresentation 564 of a cassette is shown. In this example, the cassettehas 25 wafer positions (although cassettes of different sizes may beaccommodated). For a given type of cassette, data is input into thecomputer to indicate the number of wafer slots and the positioningbetween the wafer slots so that the computer can control indexing of thecassette. In FIG. 19, again, the specific slots are numbered 1-25. Inaddition, visual indicators are provided to inform the operator of thecondition of the various wafers in the slots. In the example depicted inFIG. 19, slots 6, 9 and 15 are shown blank. This corresponds to thesystem determining that no wafers were present in these slots of thecassette. The slots with a plus indicia indicate those wafers which havepassed the edge defect testing procedure. The slots 5, 10 and 21 containX's to indicate wafers that have failed the edge defect testing. Othervisual indicia may be provided. For example, failed wafers may be markedin a particular color such as red, passed wafers in a particular colorsuch as green and again missing wafers in an alternative color or shownas empty slots.

FIGS. 20-24 illustrate one suitable control sequence for the abovedescribed embodiments of a wafer edge defect sensor apparatus. Thissequence is readily apparent from the flow chart.

In one suitable approach, upon powering up of the system, the computerconfirms that the wafer drive assembly 70 is off and in a loweredposition and also that the platform 20 is shifted to the unload/loadposition. In addition, one can exit the system at any time using an exitcommand with the computer then causing the shutting off the wafer drivemotor, the lowering of the wafer drive and the return of the cassette tothe load/unload position.

The procedure set forth in FIGS. 20-24 may be varied but again providesone specific approach which may be utilized. For example, the presenceof a wafer in a slot may be detected in a number of ways. In thedisclosed flow chart, a specific approach involves commencing therotation of the drive 70. If a wafer notch detect sensor “off” signal isnot determined within a particular time, for example within one fourthof a second of energizing the drive motor, then it is assumed that thereis no wafer in this slot of the cassette. The system sequences to placethe next wafer slot in a position for testing. In the event initiallifting of the cover is sensed, the wafer drive lifter is lowered, thewafer drive motor is stopped and the defect and notch sensor/detectorsare turned off. Consequently, operators are not exposed to moving partswhen the cover is lifted. Sensing of the presence of the cassette in theunit involves a determination of whether the cassette is in theunload/load position. Similarly, the cassette presence sensor providesan indication that the cassette has been properly placed in theapparatus. Processing of the wafers does not commence until the door isclosed. In addition, the cassette is not indexed to place the first slotin position for evaluation of a wafer contained in the slot until thewafer drive lifter has been lowered to place it out of the way of thecassette. As the cassette is indexed to successive wafer slot positions(and under the computer control the user may specify that certain slotpositions be skipped as the user may know that certain positions have nowafers), the system is monitored to determine if the cassette is at thedesired position. When the cassette is at the desired position, thewafer lifter is raised and rotation of the wafer drive commences. If awafer is present in the wafer slot, the system watches for the detectionof the notch or other wafer position indicia. When this occurs, data issampled until the wafer position indicia is re-detected. The rotation ofthe drive is then stopped and data is stored and/or processed.Eventually the last wafer slot position and a wafer (if any) containedtherein is checked. The wafer drive motor is then stopped and the waferlifter is lowered. The wafer cassette is then returned to theload/unload position and the operator is alerted that the process iscomplete.

In the above system, the computer may also be controlled to rotate aparticular wafer to a given position as directed by an operator.

Numerous modifications may be made to the electronic media edge defectdetection apparatus described above. We claim as our invention all suchmodifications. For example, multiple wafers may be simultaneouslyexamined by the addition of additional idler arms, sensor assemblies anddrive roll mechanisms to the apparatus. For example, in the case of a25-position cassette, five such devices may be used and spaced apart totest five wafers at a time. FIG. 25 shows an alternative form of sensorassembly designated 30A utilizing two light emitters and a singledetector focusing on one side edge margin of the wafer 21, two lightemitters and a single detector focused on the opposite side edge marginof the wafer 21 and optionally (not shown) a third set of two lightemitters and a single detector focused on the outer edge of the wafer21. In this example monitoring of defects at the outer edge of the wafermay be eliminated (this approach may also be used in the previouslydescribed embodiments). In the form shown in FIG. 26, although lessdesirable, light from a single light emitter is reflected off a firstside edge margin of the wafer 21 to a single detector; light from asecond light emitter is reflected off of the opposite side edge of thewafer to a single detector; with a similar arrangement optionally beingused to monitor the outer edge of the wafer. The amount of light thatreaches the detectors in FIG. 26 is affected by the defects as defectstend to scatter the light away from being reflected to the detectors.The embodiment of FIG. 26 is less desirable. In addition, the embodimentof FIG. 25 eliminates the redundancy provided by multiple emitters anddetectors along each of the edge margins of a wafer and the benefitsfrom such redundancy as previously described. Nevertheless, variationssuch as these illustrate the fact that the present invention is notlimited to the specifically described embodiments.

We claim:
 1. A method of determining the presence of defects along theedge of electronic media, the electronic media having first and secondopposed side edge margins and an outer edge margin extending between thefirst and second side edge margins, the method comprising: deliveringlight from at least one first light source to a first portion of thefirst side edge margin of the media; delivering light from at least onesecond light source to a first portion of the second side edge margin ofthe media; delivering light from at least one third light source to afirst portion of the outer edge margin of the media; positioning atleast one first detector to detect a portion of the light delivered tothe first portion of the first side edge margin that has been deflectedby the first portion of the first side edge margin toward the at leastone first detector, the at least one first detector providing a firstoutput corresponding to the detected light which is detected by the atleast one first detector; positioning at least one second detector todetect a portion of the light delivered to the first portion of thesecond side edge margin that has been deflected by the first portion ofthe second side edge margin toward the at least one second detector, theat least one second detector providing a second output corresponding tothe detected light which is detected by the at least one seconddetector; positioning at least one third detector to detect a portion ofthe light delivered to the first portion of the outer edge margin thathas been deflected by the first portion of the outer edge margin towardthe at least one third detector, the at least one third detectorproviding a third output corresponding to the detected light which isdetected by the at least one third detector; moving the electronic mediarelative to the at least one first light source, the at least one firstdetector, the at least one second source, the at least one seconddetector; the at least one third light source and the at least one thirddetector; processing the respective detector outputs to determine thepresence of defects at the first and second side edge margins and outeredge of the electronic media; and indicating the presence of suchdefects.
 2. A method according to claim 1 wherein there are at least twoof said first light sources; at least two of said second light sourcesand at least two of said third light sources.
 3. A method according toclaim 1 including the act of adjusting the intensity of light from therespective at least one first, second and third light sources.
 4. Amethod according to claim 3 comprising the act of automatically andindependently adjusting the intensity of light from the at least onerespective first, second and third light sources.
 5. A method accordingto claim 1 further comprising: delivering light from at least one fourthlight source to a second portion of the first side edge margin of themedia, the second portion being spaced in a first direction from thefirst portion of the first side edge margin of the media; deliveringlight from at least one fifth light source to a second portion of thesecond side edge margin of the media, the second portion being spaced inthe first direction from the first portion of the second side edgemargin of the media; delivering light from at least one sixth lightsource to a second portion of the outer edge margin of the media, thesecond portion being spaced in the first direction from the firstportion of the outer edge margin of the media; positioning at least onefourth detector to detect a portion of the light delivered to the secondportion of the first side edge margin that has been deflected by thesecond portion of the first side edge margin toward the at least onefourth detector, the at least one fourth detector providing a fourthoutput corresponding to the detected light which is detected by the atleast one fourth detector; positioning at least one fifth detector todetect a portion of the light delivered to the second portion of thesecond side edge margin that has been deflected by the second portion ofthe second side edge margin toward the at least one fifth detector, theat least one fifth detector providing a fifth output corresponding tothe detected light which is detected by the at least one fifth detector;positioning at least one sixth detector to detect a portion of the lightdelivered to the second portion of the outer edge margin that has beendeflected by the second portion of the outer edge margin toward the atleast one sixth detector, the at least one sixth detector providing asixth output corresponding to the detected light which is detected bythe at least one sixth detector; and wherein the act of moving theelectronic media comprises moving the electronic media relative to theat least one fourth light source, the at least one fourth detector, theat least one fifth light source, the at least one fifth detector, the atleast one sixth light source and the at least one sixth detector.
 6. Amethod according to claim 5 wherein there are at least two of saidfirst, second, third, fourth, fifth and sixth light sources.
 7. A methodaccording to claim 1 wherein the acts of delivering light from therespective light sources comprise the acts of delivering light fromlight sources which comprise LEDs.
 8. A method according to claim 1further comprising the acts of: delivering light from at least oneseventh light source to a third portion of the first side edge margin ofthe media, the third portion of the first side edge margin beingpositioned closer to the first portion of the outer edge margin of themedia than the first portion of the first side edge margin; deliveringlight from at least one eighth light source to a third portion of thesecond side edge margin of the media, the third portion of the secondside edge margin of the media being closer to the first portion of theouter edge margin than the first portion of the second side edge marginof the media; positioning at least one seventh detector to detect aportion of the light delivered to the third portion of the first sideedge margin that has been deflected by the third portion of the firstside edge margin toward the at least one seventh detector, the at leastone seventh detector providing a seventh output corresponding to thedetected light which is detected by the at least one seventh detector;positioning at least one eighth detector to detect a portion of thelight delivered to the third portion of the second side edge margin thathas been deflected by the third portion of the second side edge margintoward the at least one eighth detector, the at least one eighthdetector providing an eighth output corresponding to the detected lightwhich is detected by the at least one eighth detector; and wherein theact of moving the electronic media further comprises the act of movingthe electronic media relative to the at least one seventh light source,the at least one seventh detector, the at least one eighth light sourceand the at least one eighth detector.
 9. A method according to claim 8wherein there are at least two of the seventh and eighth light sources.10. A method according to claim 8 further comprising: delivering lightfrom at least one ninth light source to a fourth portion of the firstside edge margin of the media, the fourth portion being positionedcloser to the second second portion of the outer edge margin than theportion of the first side edge margin of the media; delivering lightfrom at least one tenth light source to a fourth portion of the secondside edge margin of the media, the fourth portion of the second sideedge margin of the media being closer to the second portion of the outeredge margin than the second portion of the second side edge margin ofthe media; positioning at least one ninth detector to detect a portionof the light delivered to the fourth portion of the first side edgemargin that has been deflected by the fourth portion of the first sideedge margin toward the at least one ninth detector, the at least oneninth detector providing a ninth output corresponding to the detectedlight which is detected by the at least one ninth detector; positioningat least one tenth detector to detect a portion of the light deliveredto the fourth portion of the second side edge margin that has beendeflected by the fourth portion of the second side edge margin towardthe at least one tenth detector, the at least one tenth detectorproviding a tenth output corresponding to the detected light which isdetected by the at least one tenth detector; and wherein the act ofmoving the electronic media comprises the act of moving the electronicmedia relative to the at least one ninth light source, the at least oneninth detector, the at least one tenth light source and the at least onetenth detector.
 11. A method according to claim 10 wherein there are atleast two of said ninth light sources and at least two of said tenthlight sources.
 12. A method according to claim 1 further comprising theacts of: lifting the electronic media and wherein the act of moving theelectronic media comprises the act of moving the lifted electronic mediaat least during a portion of the time the electronic media is lifted,and further comprising the act of lowering the electronic media.
 13. Amethod according to claim 1 wherein the act of processing the detectedlight comprises the act of determining the first derivative of changesin the respective detector outputs and comparing the first derivative ofsuch changes to a threshold.
 14. A method according to claim 1comprising the act of tracking the position of the media as it is movedand correlating the position of the media with the detected defects suchthat the location of the defects is determined and wherein theindicating act comprises the act of indicating the presence of suchdefects.
 15. A method according to claim 1 wherein the media includes aposition indicator and wherein the method of processing the detect oroutputs comprises the act of ignoring light detected at least at thelocation of the position indicator.
 16. A method according to claim 15wherein the act of ignoring comprises the act of ignoring light detectedfrom locations at either side of the position indicator and at thelocation of the position indicator.
 17. A method according to claim 1wherein the act of moving the electronic media comprises the act ofturning a disk.
 18. A method according to claim 1 wherein the act ofindicating the presence of defects comprises the act of indicating thosedisks in a cassette of disks which contain an unacceptable level ofdefects.
 19. A method of determining the presence of defects along theedge of electronic media, the electronic media having first and secondopposed side edge margins and an outer edge margin extending between thefirst and second side edge margins, the method comprising: moving themedia; directing light from plural light sources toward the first sideedge margin of the media at least during a portion of the time that themedia is moving; directing light from plural light sources toward thesecond side edge margin of the media at least during a portion of thetime that the media is moving, the light being directed from plurallight sources toward the second side edge margin of the mediasimultaneously with the light being directed from plural light sourcestoward the first side edge margin of the media; detecting lightscattered from the media toward plural detectors; and determining thepresence of defects from the detected light.
 20. A method of determiningthe presence of defects along the edge of electronic media, theelectronic media having first and second opposed side edge margins andan outer edge margin extending between the first and second side edgemargins, the method comprising: moving the media; directing light fromplural light sources toward the first side edge margin of the media atleast during a portion of the time that the media is moving; directinglight from plural light sources toward the second side edge margin ofthe media at least during a portion of the time that the media ismoving; further comprising the act of directing light from plural lightsources toward the outer edge margin of the media during at least aportion of the time that the media is moving; detecting light scatteredfrom the media toward plural detectors; and determining the presence ofdefects from the detected light.
 21. A method according to claim 20 inwhich the acts of directing light comprises directing light throughrespective elongated light directing bores and the act of detectinglight comprises the act of detecting light passing through respectiveelongated light detecting bores.
 22. A method of determining thepresence of defects along the edge of electronic media, the electronicmedia having first and second opposed side edge margins and an outeredge margin extending between the first and second side edge margins,the method comprising: moving the media; directing light from plurallight sources toward the first side edge margin of the media at leastduring a portion of the time that the media is moving; directing lightfrom plural light sources toward the second side edge margin of themedia at least during a portion of the time that the media is moving andreceiving light directed from the light sources directed toward thefirst side edge margin of the media and without interrupting themovement of the media between the act of directing light from plurallight sources toward the first side edge margin of the media and the actof directing light from plural light sources toward the second side edgemargin of the media; detecting light scattered from the media towardplural detectors; and determining the presence of defects from thedetected light.
 23. A method of determining the presence of defectsalong the edge of electronic media, the electronic media having firstand second opposed side edge margins and an outer edge margin extendingbetween the first and second side edge margins, the method comprising:moving the media; directing light from a first set of plural lightsources toward the first side edge margin of the media at least during aportion of the time that the media is moving; directing light from asecond set of plural light sources toward the second side edge margin ofthe media at least during a portion of the time that the media is movingand receiving light directed from the first set of plural light sourcesand without inverting the media to position the second side edge marginto receive light from the second set of plural light sources; detectinglight scattered from the media toward plural detectors; and determiningthe presence of defects from the detected light.